We determined the amino acid sequence of RS viral M protein was deduced from the cDNA sequence of a recombinant plasmid harboring the gene. The RS viral cDNA insert of 950 nucleotides had a poly(A) tail at one end. The other end corresponding to the 5' end of the mRNA lacked five nucleotides (NGGGC) of the mRNA. The cDNA sequence had an open reading frame capable of encoding a protein of 28717 dal (256 amino acids). The protein was relatively basic and moderately hydrophobic. It did not contain regions homologous to other viral matric proteins. A second open reading frame potentially encoding a protein of 75 amino acids was also present a the 3' end of the sDNA insert. This overlapped the first reading frame by 20 amino acids. Several recombinant plasmids containing cDNA encoding the RS viral phosphoprotein gene were identified by a variety of methods. pRSA3, encoding RS viral P protein was selected for sequencing. It has 916 bp of R3 viral sequence including a poly A tail, of 14 residues. It lacked the NGGG . . . sequence corresponding to the 5' end of the mRNA. As with other RS viral genes this is part of the conserved sequence 5' NGGGCAAAT. Starting at position 18, there is a single long open reading frame encoding a protein of 241 amino acids with a molecular weight of 27150. It lacks sequence homology with Sendai virus P protein or VSV NS protein which represent counterparts of RS P protein. Unlike the situation reported for Sendai and measles viruses, this gene does not have a second reading frame capable of encoding another protein.